(core) Simple localization support and currency selector.

Summary:
- Grist document has a associated "locale" setting that affects how currency is formatted.
- Currency selector for number format.

Test Plan: not done

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D2977

app/client/widgets/CurrencyPicker.ts

@@ -0,0 +1,49 @@
+import {ACSelectItem, buildACSelect} from "app/client/lib/ACSelect";
+import {Computed, IDisposableOwner, Observable} from "grainjs";
+import {ACIndexImpl} from "app/client/lib/ACIndex";
+import {testId} from 'app/client/ui2018/cssVars';
+import {currencies} from 'app/common/Locales';
+
+interface CurrencyPickerOptions {
+  // The label to use in the select menu for the default option.
+  defaultCurrencyLabel: string;
+}
+
+export function buildCurrencyPicker(
+  owner: IDisposableOwner,
+  currency: Observable<string|undefined>,
+  onSave: (value: string|undefined) => void,
+  {defaultCurrencyLabel}: CurrencyPickerOptions
+) {
+  const currencyItems: ACSelectItem[] = currencies
+    .map(item => ({
+      value: item.code,
+      label: `${item.code} ${item.name}`,
+      cleanText: `${item.code} ${item.name}`.trim().toLowerCase(),
+    }));
+
+  // Add default currency label option to the very front.
+  currencyItems.unshift({
+    label : defaultCurrencyLabel,
+    value : defaultCurrencyLabel,
+    cleanText : defaultCurrencyLabel.toLowerCase(),
+  });
+  // Create a computed that will display 'Local currency' as a value and label
+  // when `currency` is undefined.
+  const valueObs = Computed.create(owner, (use) => use(currency) || defaultCurrencyLabel);
+  const acIndex = new ACIndexImpl<ACSelectItem>(currencyItems, 200, true);
+  return buildACSelect(owner,
+    {
+      acIndex, valueObs,
+      save(_, item: ACSelectItem | undefined) {
+        // Save only if we have found a match
+        if (!item) {
+          throw new Error("Invalid currency");
+        }
+        // For default value, return undefined to use default currency for document.
+        onSave(item.value === defaultCurrencyLabel ? undefined : item.value);
+      }
+    },
+    testId("currency-autocomplete")
+  );
+}